• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

1990 4.0 auto misfire at 1700rpm

Spydie

NAXJA Forum User
Location
Michigan
About to pick up a 1990 comanche with a 4.0 auto in it but am leary as it has a slight misfire at 1700rpm. The engine was just rebuilt by an actual engine machine shop so its not a garage build. The engine was bored out .020", over sized pistons, new rods, has cleggs stage 1 cam and cleggs stage 2 head. The engine has maybe 50 miles on it after the rebuild so its still in its break in period. Am wondering before i get this, what might the general causes be? Would like to know how little or big of an issue it might be.

Edit: When i went and looked at the truck the engine would only misfire once. Owner says its a crap shoot on if it will happen or not any given day
 
My bet would be on an injector that dried out and is clogged, but before I bought anything I would do a wet/dry compression check. I would take my endoscope and look down the cylinders.

An oil assay should show you if there is any metal in the oil.

A question would be if they used any breakin lube on the cam before starting it up. The assay should show that up as long as they haven't done an oil change.
 
Back
Top